WebSockets & Real-Time Systems with Spring · Lesson

Private Messaging with STOMP

Learn to implement direct, one-on-one private messaging between users using STOMP's user destinations.

Private Messaging with STOMP is a free WebSockets & Real-Time Systems with Spring lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the WebSockets & Real-Time Systems with Spring learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Private Chat Essentials

Welcome! In this lesson, we'll learn how to build private messaging functionality into our chat application using WebSockets and STOMP.

Unlike public chat rooms where everyone receives messages, private messages (like direct messages or DMs) are sent specifically from one user to another. This requires a way to route messages directly to an individual's unique session.

STOMP User Destinations

STOMP provides a special destination prefix: /user. When a client subscribes to a destination like /user/queue/private-messages, the STOMP broker (and Spring) automatically translate this into a unique, session-specific queue for that particular authenticated user.

/user prefix: Indicates a user-specific destination.
Unique per user: Each user gets their own 'inbox' for private messages.
Abstracted routing: You don't need to know the actual session ID.

Spring & User Routes

Spring's WebSocket and STOMP integration works hand-in-hand with the /user prefix. When you configure your message broker, you tell Spring to enable user destinations:

config.setUserDestinationPrefix("/user");

This setting ensures that messages addressed to /user/{username}/queue/{destination} are correctly routed by Spring to the WebSocket session(s) associated with {username}.

Server-Side: Sending Private Messages

On the server, Spring provides the SimpMessagingTemplate. This powerful tool allows you to send messages to various STOMP destinations, including user-specific ones.

The key method for private messaging is convertAndSendToUser(). It takes three main arguments:

username: The identifier of the recipient user.
destination: The specific queue within that user's private space (e.g., /queue/private-messages).
payload: The actual message content.

Server Private Send Demo

Try running this simplified Spring Boot application. It shows a controller method that sends a private message using SimpMessagingTemplate. Remember, in a real app, the recipient's username would come from the client's message payload or other context.

package com.coddykit;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Configuration;
import org.springframework.messaging.handler.annotation.MessageMapping;
import org.springframework.messaging.simp.SimpMessagingTemplate;
import org.springframework.messaging.simp.config.MessageBrokerRegistry;
import org.springframework.stereotype.Controller;
import org.springframework.web.socket.config.annotation.EnableWebSocketMessageBroker;
import org.springframework.web.socket.config.annotation.StompEndpointRegistry;
import org.springframework.web.socket.config.annotation.WebSocketMessageBrokerConfigurer;
import java.security.Principal;

@SpringBootApplication
@EnableWebSocketMessageBroker
public class PrivateChatApp {

    public static void main(String[] args) {
        SpringApplication.run(PrivateChatApp.class, args);
    }

    @Configuration
    static class WsConfig implements WebSocketMessageBrokerConfigurer {
        @Override
        public void configureMessageBroker(MessageBrokerRegistry cfg) {
            cfg.enableSimpleBroker("/topic", "/queue");
            cfg.setApplicationDestinationPrefixes("/app");
            cfg.setUserDestinationPrefix("/user"); // Crucial for private messages
        }
        @Override
        public void registerStompEndpoints(StompEndpointRegistry reg) {
            reg.addEndpoint("/ws").withSockJS();
        }
    }

    @Controller
    static class PrivateMsgController {
        private final SimpMessagingTemplate template;

        public PrivateMsgController(SimpMessagingTemplate t) {
            this.template = t;
        }

        @MessageMapping("/sendPrivate") // Client sends to /app/sendPrivate
        public void sendPrivateMsg(String msg, Principal p) {
            String sender = p != null ? p.getName() : "anon";
            String recipient = "targetUser"; // In real app, from msg payload

            // Send to a specific user's private queue
            template.convertAndSendToUser(
                recipient,
                "/queue/private-messages", // Client subscribes here
                "From " + sender + ": " + msg
            );
            System.out.println("Sent private msg to " + recipient + " from " + sender);
        }
    }
}

Client's Private Inbox

On the client side, a user needs to subscribe to their own private destination to receive messages. If a user's principal name is 'alice', they would subscribe to:

/user/queue/private-messages

Spring automatically maps this to /queue/private-messages-user{sessionId} internally, ensuring only 'alice' receives messages sent to her.

Client-Side Subscription

Using a STOMP client library (like Stomp.js), the subscription process is straightforward:

stompClient.subscribe('/user/queue/private-messages', function(message) {
    // Handle the private message
    console.log("Received private message: " + message.body);
});

This ensures that any message sent to the currently authenticated user's /queue/private-messages destination will be received by this client.

Private Message Model

For robust private chat, your message payload should contain structured data. A typical private message model might include:

senderId: The ID of the user who sent the message.
recipientId: The ID of the user intended to receive the message.
content: The actual text or data of the message.
timestamp: When the message was sent.

This allows clients to display messages correctly, identifying who sent what to whom.

User Identity & STOMP

How does Spring know which user is 'alice' for the /user destination? It relies on the Principal object, which is usually populated by Spring Security or another authentication mechanism.

When a WebSocket connection is established, Spring associates a Principal with that session. The convertAndSendToUser() method uses the getName() of this Principal to identify the target user.

Private Message Quiz

You've learned how Spring and STOMP handle private messages. Let's test your understanding of sending them.

Private Chat Summary

Great job! You've learned the fundamentals of implementing private messaging with STOMP and Spring.

The /user destination prefix routes messages to individual users.
Spring's SimpMessagingTemplate.convertAndSendToUser() sends messages to specific user destinations.
Clients subscribe to /user/queue/{your-private-destination} to receive their DMs.
User identity (Principal) is crucial for correct routing.

This knowledge allows you to build sophisticated, personalized real-time interactions in your applications!

Frequently asked questions

Is the “Private Messaging with STOMP” lesson free?

Yes — the full text of “Private Messaging with STOMP” is free to read here on the web, and the WebSockets & Real-Time Systems with Spring course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the WebSockets & Real-Time Systems with Spring course, upgrade to CoddyKit PRO.

What will I learn in “Private Messaging with STOMP”?

Learn to implement direct, one-on-one private messaging between users using STOMP's user destinations. You practise WebSockets & Real-Time Systems with Spring with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start WebSockets & Real-Time Systems with Spring?

No prior experience is required. WebSockets & Real-Time Systems with Spring on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Private Messaging with STOMP” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this WebSockets & Real-Time Systems with Spring lesson?

Yes. Every WebSockets & Real-Time Systems with Spring lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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